1. Field of the Invention
The present invention relates to pressure sensitive adhesive tapes having good strength in the transverse direction which can be easily cut using the fingers without using any special tool or cutter.
2. Description of the Prior Art
Pressure sensitive adhesive tapes are required to have a large strength in the transverse direction of the pressure sensitive adhesive tapes, for example, where they are used for sealing the covers of cartons. Hitherto, as such pressure sensitive adhesive tapes for sealing cartons, pressure sensitive kraft paper tapes and gum tapes have been used. Where the contents of the carton are relatively heavy in weight, pressure sensitive cloth tapes and pressure sensitive adhesive tapes having a hard polyvinyl chloride film or a polypropylene film which was stretched in the lengthwise direction as a backing have been used from the standpoint of practical strength. Pressure sensitive adhesive tapes having such a plastic film as the backing have many advantages as compared with pressure sensitive adhesive tapes having a cloth or paper as the backing in that they have good water resistance, in that they are inexpensive, in that they can be produced so as to be endurable for overwrapping uses as they exhibit an resistance reisistance to lamination, and in that they are excellent in strength. However, they have the defects that it is very difficult to cut them with the fingers or they can not be cut in their transverse direction but are obliquely cut or many creases result on the cut parts even if they can be cut. Accordingly, the ability to use these pressure sensitive adhesive tapes for sealing is poor because it is necessary to use special tools or cutters. Further, since they have poor strength in the transverse direction, they are not suitable as a pressure sensitive adhesive tape which must have strength in the transverse direction such as for sealing cartons, etc.
On the other hand, it has been suggested to stretch plastic film backings in the lengthwise direction while stretching the backing in the transverse direction so that the pressure sensitive adhesive tapes are easily cut with the fingers and the strength in the transverse direction increases. However, it has been believed that such adhesive tapes produced by applying an adhesive to the ordinarily stretched backing will not be able to be practically used because they have poor strength in the lengthwise direction and that they will break during unwinding on use because they are not strong enough to endure the unwinding force. Thus the utility of such adhesive tapes has been overlooked.